1. Field of the Invention
This invention relates to reading and writing information on a storage medium, and more particularly to a method and apparatus for authenticating the medium and information stored on the medium by performing spatial measurements.
2. Description of Related Art
In many instances, it is desirable to provide a method and apparatus for storing and transporting information. In particular, many ways have been devised for encoding information on a medium which can be conveniently carried about by a person during the normal course of business. For example, credit cards, debit cards, electronic purse cards, decrementing value cards, checks, driver's licenses, identification cards, access control cards, magnetic tapes and disks, and many other such media which are small enough to be conveniently carried in a person's handbag or wallet are ubiquitous today. However, in many of the applications in which these media are intended to be used, security is an important concern. That is, it is important that only authorized organizations are capable of modifying the information stored thereon. One very common way for information to be stored on such a medium is by magnetically encoding the information. Techniques for encoding information on magnetic media have been available for many years and are now relatively inexpensive. Other techniques include optical storage techniques and printed information using relative light and dark areas, such as the uniform purchasing codes (UPCs) which are printed on the packaging of most products today. For simplicity sake, only magnetic techniques are discussed in detail. However, it will be understood that the following discussion applies equally well to other techniques for storing information.
Magnetically encoded information can easily be copied or transferred from one magnetic information storage medium to another. Unless special provisions are made to secure the information, information can be altered and re-encoded back onto the original medium or a duplicate of the original medium. If the information is used in a system for organizing financial transactions or for personal identification, then such copying, altering, and duplicating makes the person for whom the information was intended, and the organization who operates the system, vulnerable to fraud. For example, if a magnetic stripe affixed to a debit card is used to indicate how much money is currently in a personal account, modifications to that information can be used to increase the apparent balance in order to purchase goods which have a higher value than actually exists in the account. Additionally, if the card is duplicated, the same account could be used by more than one person. It should be clear that fraud could occur in a number of ways if sensitive information is not properly secured In fact fraud due to copying and modification of information magnetically encoded on portable media, such as magnetic stripe cards, is growing at an alarming rate. For example, it is estimated that the cost of fraud to the credit card industry alone will exceed one billion dollars per year before the end of the century.
A number of techniques have been proposed to authenticate both the information, and the medium on which the information is stored (commonly referred to as a "document"), in order to prevent fraud. For example, U.S. Pat. No. 4,023,204 issued to Lee, discloses using a unique magnetic coating with pre-determined alignment of the magnetic particles as the basis for authentication measurements. Thus, a code which can not be altered can be implanted into the document to authenticate the document. U.S. Pat. No. 5,336,871 issued to Colgate, discloses the use of a hologram to authenticate a substrate on which a magnetic stripe is affixed. U.S. Pat. No. 5,354,097 issued to Tel, discloses the use of overlays to authenticate information. U.S. Pat. No. 4,628,195, issued to Baus, discloses generating a security code number determined by the relative spatial positions of corresponding data in two different forms of encoded data on a card. In particular, Baus discloses using a conventional magnetic stripe as the first means for encoding data, and using embossed characters as a second means for encoding data. The relative position of the magnetic information with respect to the embossed information is used to generate a numeric security code. In addition, dyes or absorbers incorporated in a magnetic stripe have been used to attempt to encode a security identifier into the document on which the information resides.
However, each of these methods requires the use of special materials in the security process. Accordingly, none of the old documents would be usable, and all of the documents currently in use would have to be recalled and reissued using the new security process. Recalling and replacing all of the documents that are currently in use would be very costly and has hampered the widespread implementation of such technologies.
In the case of the technique disclosed by Baus, both an automatic reading method for reading the magnetic stripe, and also an automatic reading method for reading the embossed characters, are required. Therefore, there are two sub-systems required by this technique. Furthermore, readers used at the point-of-sale must preserve the spatial relationship between the magnetically stored information and the embossed characters This is a cumbersome and expensive process which is very difficult to perform at the point-of-sale. Accordingly, it may be difficult to maintain reliable operation of systems which conform to the Baus technique.
Others have attempted to overcome the above limitations when the document is a magnetic medium by employing characteristics of the magnetic signals used to store the information to authenticate both the document and the information stored thereon.
For example, U.S. Pat. No. 4,837,426 issued to Pease, discloses a method for authenticating documents by analyzing the amplitude of the magnetic signals. U.S. Pat. Nos. 5,408,505 and 5,428,683, each issued to Indeck, et al. disclose a method for authenticating documents using "noise" in the saturation region of the magnetic data. U.S. Pat. Nos. 5,235,166, and 5,430,279, each issued to Fernandez, and U.S. Pat. No. 5,254,843 issued to Hynes, each disclose a method of authenticating documents by deriving inherent temporal measurements of timing variations of the data in the reading process. All of the above mentioned methods for authenticating documents and information using characteristics of the magnetic signals have a common drawback in that variations in the motion of the document through the reading device cause variations in the characteristics used to authenticate the document, and therefore, result in errors in the authentication process. Furthermore, degradation of the reading device and the document over time due to natural wear causes the characteristics to either change, or to appear to change, causing further errors in the authentication process.
Accordingly, it would be desirable to provide a system which: (1) is capable of authenticating documents and the information stored thereon without use of a new material or process for generating the document to be authenticated; (2) is unaffected by changes in the speed at which the document moves with respect to the reader; and (3) will remain reliable over time.
In addition to the problems associated with authenticating documents and the information that is stored thereon, there is a need for methods for increasing the amount of information that can be stored on a document. For example, a magnetic stripe of a credit card is a relatively small area on which information can be stored. Accordingly, it would be advantageous to provide a method and apparatus which increases the amount of information that can be stored on a document.
Still further, in order to maintain standards for writing information on documents, it would be advantageous to be able to accurately determine the absolute distance between a transition in the information stored on a document from a first logical state to a second logical state without the need to control the velocity of the reader with respect to the document.